Green's function calculation of electron spin polarization. III. Freely diffusing radical pairs

摘要

A general analytic expression is derived for the electron spin polarization (CIDEP) generated in neutral radicals pairs in liquid solutions at high magnetic fields. It incorporates arbitrary reactivities of the singlet and triplet states of the radical pair complex, additional dephasing processes at the contact distance, and arbitrary values of the singlet-triplet mixing parameter. The exchange interaction is assumed to decrease exponentially with the separation between the radicals and is characterized by a decay length l_x and a maximum value J_0. The only condition for the applicability of the expression is that the exchange interaction is locally weak (J_0l_x~2/D)~2 1, but it may be integral strong (D is the relative diffusion constant for the radicals). By comparison with numerical results, it is shown that the expression is very accurate; no deviations were found. The expression is obtained from our previously derived general expression by explicitly evaluating all the fundamental quantities from the Green's function of the free diffusive motion. It is shown that the previously published formulas correspond to special cases of the present expression.